JP4669272B2 - Method for producing polyethylene terephthalate using bis- (2-hydroxyethyl) terephthalate as a raw material - Google Patents

Description

  It is characterized in that it is obtained by using a bis- (2-hydroxyethyl) terephthalate as a raw material without adding other polyester monomers such as terephthalic acid, and smoothly proceeding the polymerization reaction without causing blockage by a scattering oligomer. The present invention relates to a method for producing polyethylene terephthalate.

  Polyester, particularly polyethylene terephthalate (hereinafter abbreviated as PET), is widely used by being molded into fibers, films, industrial resins, bottles, cups, trays, etc. because of its excellent mechanical and chemical properties. .

  In recent years, with increasing environmental awareness, resources have been recovered from waste to save resources and reduce the amount of waste incinerated and landfilled. A number of recycling methods and recycled products have been devised for PET, and one of them is PET polymer waste that reacts with ethylene glycol in the presence of an alkali catalyst to depolymerize it, and bis- (2-hydroxyethyl) terephthalate (hereinafter referred to as PET). There is a technique of obtaining (referred to as Patent Document 1).

  However, there is a problem that the reaction is extremely slow even if an attempt is made to proceed the polymerization reaction using germanium or an antimony catalyst with BHET 100% as a raw material (see, for example, Patent Document 2). If the polymerization reaction is slow, serious problems such as clogging in the distillation system of the reactor and clogging in the distillation system of the reactor occur, resulting in a significant reduction in productivity. Therefore, it is said that the polymerization reaction can be promoted by adding 0.5 to 1 mol of terephthalic acid to BHET recovered and regenerated from PET waste to save resources (see, for example, Patent Document 2). However, when trying to obtain environmentally friendly product certification for polyester products obtained from recycled raw materials, the Eco Mark standard, for example, states that the usage rate of recycled raw materials is 50% or more, and the polymer stage Thus, a method (for example, see Patent Document 2) in which the recycled material usage rate is 50% or less is extremely disadvantageous in terms of differentiation of the final product. Also, in order to accelerate the polymerization reaction, this process involves mixing the polymer melted by adding a catalyst to BHET and the melted BHET after adding terephthalic acid to the melted BHET. As a result, the investment cost for constructing the manufacturing equipment also increases (see, for example, Patent Document 2).

WO 01/29110 Pamphlet Claim JP, 2004-231855, A Claim, Example 6

  To provide polyethylene terephthalate by smoothly proceeding a polymerization reaction without using other oligomers such as terephthalic acid and using only bis- (2-hydroxyethyl) terephthalate as a raw material and without blocking by scattered oligomers. It is in.

［上記式中、Ｒ ^１ 、Ｒ ^２ 、Ｒ ^３ 及びＲ ^４ はそれぞれ同一若しくは異なって、炭素数１〜１０のアルキル基又はフェニル基を示し、ｍは１〜４の整数を示し、かつｍが２、３又は４の場合、２個、３個又は４個のＲ ^２ 及びＲ ^３ は、それぞれ同一であっても異なっていてもどちらでもよい。］

［上記式中、Ｒ ^８ は炭素数２〜１８のアルキル基又は炭素数６〜２０のアリール基であり、ｐは１又は２であって、ｐが１の時にｑは０又は１、ｐが２の時にｑは０である。］ As a result of intensive studies in view of the above prior art, the present inventors have completed the present invention. That is, an object of the present invention is a method for producing polyethylene terephthalate in which only bis- (2-hydroxyethyl) terephthalate is polymerized using a titanium compound as a catalyst , and the titanium compound is represented by the following general formula (I). It was obtained by heating a titanium compound and a phosphorus compound represented by the following general formula (IV) in glycol in a range where the gram equivalent ratio of phosphorus atom to titanium atom (P / Ti) is 1 to 4. It can achieve by the manufacturing method of the polyethylene terephthalate of Claim 1 using a precipitate .

[Wherein R ¹ , R ² , R ³ and R ⁴ are the same or different and each represents an alkyl group having 1 to 10 carbon atoms or a phenyl group, m represents an integer of 1 to 4, and m represents In the case of 2, 3 or 4, 2, 3 or 4 R ² and R ³ may be the same or different from each other. ]

[In the above formula, R ⁸ is an alkyl group having 2 to 18 carbon atoms or an aryl group having 6 to 20 carbon atoms, p is 1 or 2, and when p is 1, q is 0 or 1, and p is When 2, q is 0. ]

  According to the method of the present invention, polyethylene terephthalate can be obtained at a good polymerization rate using only polyethylene terephthalate made from bis- (2-hydroxyethyl) terephthalate as a raw material and without adding other polyester monomers such as terephthalic acid. . In addition, the polymerization reaction can proceed smoothly without being blocked by scattered oligomers.

  In the present invention, it is necessary to use bis- (2-hydroxyethyl) terephthalate (BHET). BHET is not particularly limited. For example, BHET may be produced by direct esterification from terephthalic acid and ethylene glycol (EG), produced by transesterification from dimethyl terephthalate (DMT) and EG, or new What was produced | generated by depolymerizing used collection | recovery PET, such as waste PET and a drink bottle which generate | occur | produce in the step which manufactures a PET product with EG, may be used. From the viewpoint of resource saving and the like, it is preferable to use at least a part obtained from a depolymerized product generated by depolymerizing recovered PET with EG.

  The depolymerized product (crude BHET) produced by depolymerizing the recovered PET with EG is used in the preliminary reaction step and the polymerization step after being purified BHET through at least a purification step for distillation purification. Is preferred.

  Here, in the depolymerization product (crude BHET) produced by depolymerizing the collected PET with EG, additives such as a polymerization catalyst and a colorant contained in the collected PET remain ( Since most of the additives remain in the form of cations and anions), the PET obtained is colored yellowish brown unless special attention is paid to the purification of the crude BHET. Therefore, in the purification step, it is preferable that the decolorization / deionization step for removing the colorant, anion / cation and the like from the crude BHET as the depolymerization product is performed before the distillation step for purification by distillation operation.

  In the decolorization step, the crude BHET can be decolorized by contacting with a known decolorizing agent (for example, activated carbon or white clay). In the deionization step, the metal cation and its counter anion can be removed from the crude BHET by bringing the crude BHET into contact with a cation exchange resin and / or an anion exchange resin.

  Here, if the ion content in the crude BHET (the total content of anions and cations. The same applies hereinafter) is 100 ppm by mass or more, there is a risk of adverse effects during distillation purification, and if it exceeds 50 ppm by mass. It becomes difficult to obtain PET having good quality such as color tone. For this reason, in the said deionization process, it is preferable to deionize so that the ion content in crude BHET may be 50 mass ppm or less.

  In the distillation step for purification by the distillation operation, the method for removing EG from the crude BHET EG solution is not particularly limited. However, due to the chemical nature of BHET, if the distillation is not performed at the lowest possible temperature and in the shortest possible time, undesired polymerization may proceed during residence or evaporation in the still. Therefore, in this distillation step, it is preferable to use a molecular distiller in order to remove EG in a shorter time and at a lower temperature.

  An example of a factor indicating the degree of purification of purified BHET obtained through the purification process is the color tone of BHET. For example, the hue b value in the display method according to ASTM-D1482-57T is a value measured with a color difference meter. It is preferably 3 or less, and more preferably 1.0 or less. When PET is produced from BHET having a hue b value exceeding 3, the hue b value of PET greatly exceeds 5, and the practical use cannot be practically achieved. Subsequently, polyethylene terephthalate is produced from the thus obtained BHET by a polymerization process as shown below.

  This polymerization step can be performed, for example, as follows. First, a predetermined amount of BHET and a titanium compound serving as a catalyst are placed in a polymerization vessel under a nitrogen atmosphere, and the temperature is preferably raised to 130 to 200 ° C. with stirring to bring BHET into a molten state. The liquid is added at once or gradually and mixed. And the temperature of a reaction system is gradually raised to about 230-245 degreeC under a normal pressure, the low boiling component containing EG and water byproduced is distilled off, and it confirms that the evaporation stops. Thereafter, the temperature is further increased and the reaction system is gradually depressurized while maintaining the polymerization reaction temperature of about 260 to 290 ° C., and finally the internal pressure is lowered to about 10 to 80 Pa. The melt viscosity of the reactant in the system gradually increases, and the polymerization reaction is terminated when the viscosity reaches a predetermined viscosity (for example, it can be confirmed by electric power consumed for stirring). The production method of the present invention is characterized in that, in this polymerization step, terephthalic acid or the like is not newly added between the process start time and the process end time.

  After the polyethylene terephthalate obtained in this way is pelletized, it may be further subjected to polycondensation in a solid phase polymerization step as necessary. Any known method can be used for the solid phase polymerization method. May be. Furthermore, when manufacturing these polyethylene terephthalates, you may use another additive, for example, a coloring agent, an antioxidant, a ultraviolet absorber, an antistatic agent, a flame retardant, etc. as needed.

  On the other hand, in the present invention, it is necessary to use a titanium compound as a polymerization catalyst. Examples of the titanium compound include tetraalkoxy titanium and tetraphenoxy titanium having an alkyl group having 1 to 10 carbon atoms. As a more specific compound example of tetraalkoxytitanium, tetraisopropoxytitanium, tetrapropoxytitanium, tetra-n-butoxytitanium, tetraethoxytitanium, tetraphenoxytitanium, octaalkyltrititanate, or hexaalkyldititanate are preferable. Can be mentioned. Thus, the subject of this invention can be solved by using a titanium compound only with BHET as a raw material.

  Further, the polycondensation catalyst of the titanium compound used in the present invention is represented by the titanium compound represented by the following general formula (I), or the titanium compound represented by the following general formula (I) and the following general formula (II). It is also possible to use a polymerization catalyst system comprising a titanium compound component containing at least one selected from the group consisting of products obtained by reacting aromatic polycarboxylic acids or anhydrides thereof.

［上記式中、Ｒ^１、Ｒ^２、Ｒ^３及びＲ^４はそれぞれ同一若しくは異なって、炭素数１〜１０のアルキル基又はフェニル基を示し、ｍは１〜４の整数を示し、かつｍが２、３又は４の場合、２個、３個又は４個のＲ^２及びＲ^３は、それぞれ同一であっても異なっていてもどちらでもよい。］

[Wherein R ¹ , R ² , R ³ and R ⁴ are the same or different and each represents an alkyl group having 1 to 10 carbon atoms or a phenyl group, m represents an integer of 1 to 4, and m represents In the case of 2, 3 or 4, 2, 3 or 4 R ² and R ³ may be the same or different from each other. ]

［上記式中、ｎは２〜４の整数を表わす。］

[In the above formula, n represents an integer of 2 to 4. ]

  Here, as the titanium compound represented by the general formula (I), specifically, tetraisopropoxy titanium, tetrapropoxy titanium, tetra-n-butoxy titanium, tetraethoxy titanium, tetraphenoxy titanium, octaalkyl trititanate, Or hexaalkyl dititanate is preferably used.

  In addition, the aromatic polyvalent carboxylic acid represented by the general formula (II) to be reacted with the titanium compound or an anhydride thereof includes phthalic acid, trimellitic acid, hemimellitic acid, pyromellitic acid, or an anhydride thereof. Is preferably used.

  In the case of reacting the titanium compound with an aromatic polyvalent carboxylic acid or an anhydride thereof, a part or all of the aromatic polyvalent carboxylic acid or an anhydride thereof is dissolved in a solvent, and the titanium compound is dissolved in the mixed solution. It is carried out by dripping and heating at a temperature of 0-200 ° C. for at least 30 minutes, preferably at a temperature of 30-150 ° C. for 40-90 minutes. There is no restriction | limiting in particular about the reaction pressure in this case, A normal pressure is enough.

  As a solvent for dissolving the aromatic polyvalent carboxylic acid or its anhydride, any of ethanol, ethylene glycol, trimethylene glycol, tetramethylene glycol, benzene, xylene and the like can be used as desired.

  Here, the reaction molar ratio between the titanium compound and the aromatic polyvalent carboxylic acid or its anhydride is not particularly limited, but if the proportion of the titanium compound is too high, the color tone of the resulting polyester deteriorates, or the softening point. On the contrary, if the proportion of the titanium compound is too low, the polymerization reaction may be difficult to proceed. For this reason, it is preferable that the reaction molar ratio of a titanium compound and aromatic polyvalent carboxylic acid or its anhydride shall be in the range of 2/1-2/5. Also, there is no particular limitation as long as the above titanium compound can be reacted with the aromatic polyvalent carboxylic acid or its anhydride under other conditions.

  The polymerization catalyst system used as the polymerization catalyst in the present invention may further comprise an unreacted mixture of the above-described titanium compound or titanium compound component and a phosphorus compound represented by the following general formula (III). good.

［上記式中、Ｒ^５、Ｒ^６及びＲ^７は、同一又は異なって炭素原子数１〜４のアルキル基を示し、Ｘは、−ＣＨ_２−又は―ＣＨ（Ｙ）−を示す（Ｙは、ベンゼン環を示す）。］

[Wherein, R ⁵ , R ⁶ and R ⁷ are the same or different and each represents an alkyl group having 1 to 4 carbon atoms, X represents —CH ₂ — or —CH (Y) — (Y represents Represents a benzene ring). ]

  Examples of the phosphorus compound include carbomethoxymethanephosphonic acid, carboethoxymethanephosphonic acid, carbopropoxymethanephosphonic acid, carboptoxymethanephosphonic acid, carbomethoxy-phosphono-phenylacetic acid, carboethoxy-phosphono-phenylacetic acid, carboprotoxy It is preferably selected from dimethyl esters, diethyl esters, dipropyl esters or dibutyl esters of phosphono-phenylacetic acid or carbobutoxy-phosphono-phenylacetic acid.

  Since the above phosphorus compound reacts relatively slowly with a titanium compound or a titanium compound component (hereinafter abbreviated as “titanium compound etc.”) as compared with a phosphorus compound usually used as a stabilizer, When the catalyst activity duration of the titanium compound or the like during the reaction is long, as a result, the amount of the titanium compound added to the polyester can be reduced, and when a large amount of stabilizer is added to the catalyst as in the present invention Even so, the heat stability of the polyester is hardly impaired.

  The above phosphorus compound is preferably in the range of 5 to 80 mmol% in terms of phosphorus element. If the phosphorus compound is less than 5 mmol%, the color tone of the polyester tends to decrease, and if it exceeds 80 mmol%, the polymerization reaction is difficult to proceed, which is not preferable. The addition amount of the phosphorus compound is more preferably in the range of 10 to 60 mmol%.

  On the other hand, as a polycondensation catalyst for the titanium compound used in the present invention, a titanium compound represented by the following general formula (I) and a phosphorus compound represented by the following general formula (IV) A titanium / phosphorus reactant which is a precipitate obtained by heating in glycol in an equivalent ratio (P / Ti) of 1 to 4 can also be used.

［上記式中、Ｒ^１、Ｒ^２、Ｒ^３及びＲ^４はそれぞれ同一若しくは異なって、炭素数１〜１０のアルキル基又はフェニル基を示し、ｍは１〜４の整数を示し、かつｍが２、３又は４の場合、２個、３個又は４個のＲ^２及びＲ^３は、それぞれ同一であっても異なっていてもどちらでもよい。］

[Wherein R ¹ , R ² , R ³ and R ⁴ are the same or different and each represents an alkyl group having 1 to 10 carbon atoms or a phenyl group, m represents an integer of 1 to 4, and m represents In the case of 2, 3 or 4, 2, 3 or 4 R ² and R ³ may be the same or different from each other. ]

［上記式中、Ｒ^８は炭素数２〜１８のアルキル基又は炭素数６〜２０のアリール基であり、ｐは１又は２であって、ｐが１の時にｑは０又は１、ｐが２の時にｑは０である。］

[In the above formula, R ⁸ is an alkyl group having 2 to 18 carbon atoms or an aryl group having 6 to 20 carbon atoms, p is 1 or 2, and when p is 1, q is 0 or 1, and p is When 2, q is 0. ]

  Here, when the gram equivalent ratio of phosphorus atom to titanium atom (P / Ti) is less than 1, the color tone of the resulting polyester is unfavorable and its heat resistance may be lowered. This is not preferable because the catalyst activity for the polyester formation reaction becomes insufficient. The gram equivalent ratio of phosphorus atoms to titanium atoms (P / Ti) is preferably in the range of 1.2 to 3.5, and more preferably in the range of 1.5 to 3.0.

  Moreover, the catalyst preparation of the titanium compound (I) and the phosphorus compound (IV) needs to be heated in glycol. Examples of the glycol include ethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. Alternatively, a mixed solvent of these and other compounds may be used. As a specific reaction method, for example, a component composed of phosphorus compound (IV) and ethylene glycol or a mixed solution of ethylene glycol and another compound are mixed, and part or all of the phosphorus compound is dissolved in a solvent, The titanium compound (I) or a solution thereof is dropped into this mixed solution, and the reaction system is heated to a temperature of 0 ° C. to 200 ° C. for 30 minutes or more, preferably 60 to 150 ° C. for 40 to 90 minutes. Is called. Or conversely, the titanium compound (I) may be dissolved in glycols, and the phosphorus compound (IV) or a solution thereof may be dropped. In this reaction, the reaction pressure is not particularly limited and is usually carried out under normal pressure.

  Examples of the titanium compound represented by the above formula (I) include titanium tetraalkoxides such as titanium tetrabutoxide, titanium tetraisopropoxide, titanium tetrapropoxide, titanium tetraethoxide, octaalkyltrititanate, and hexaalkyl. Examples include dititanate, alkyl titanate, and titanium acetate.

  In addition, as the phosphorus compound represented by the above formula (IV), when q in the formula is 0, for example, phenylphosphonic acid, methylphosphonic acid, ethylphosphonic acid, propylphosphonic acid, isopropylphosphonic acid, butylphosphonic acid, tolyl Phosphonic acid, xylylphosphonic acid, biphenylphosphonic acid, naphthylphosphonic acid, anthrylphosphonic acid, 2-carboxyphenylphosphonic acid, 3-carboxyphenylphosphonic acid, 4-carboxyphenylphosphonic acid, 2,3-dicarboxyphenylphosphonic Acid, 2,4-dicarboxyphenylphosphonic acid, 2,5-dicarboxyphenylphosphonic acid, 2,6-dicarboxyphenylphosphonic acid, 3,4-dicarboxyphenylphosphonic acid, 3,5-dicarboxyphenylphosphonic acid Acid, 2,3,4-tricarboxyl Nylphosphonic acid, 2,3,5-tricarboxyphenylphosphonic acid, 2,3,6-tricarboxyphenylphosphonic acid, 2,4,5-tricarboxyphenylphosphonic acid, 2,4,6-tricarboxyphenylphosphonic acid Among them, monoarylphosphonic acid is preferable.

  When q is 1, for example, monomethyl phosphate, monoethyl phosphate, monotrimethyl phosphate, monobutyl phosphate, monohexyl phosphate, monoheptyl phosphate, monononyl phosphate, monodecyl phosphate, monododecyl phosphate, monophenyl phosphate, mono Benzyl phosphate, mono (4-dodecyl) phenyl phosphate, mono (4-methylphenyl) phosphate, mono (4-ethylphenyl) phosphate, mono (4-propylphenyl) phosphate, mono (4-dodecylphenyl) phosphate, monotolyl Examples include phosphate, monoxyl phosphate, monobiphenyl phosphate, mononaphthyl phosphate, monoanthryl phosphate and the like.

  A method in which the titanium compound represented by the above formula (I) is reacted with a polyvalent carboxylic acid of the following formula (II) and / or an anhydride thereof is also preferably used. In that case, the reaction molar ratio of the titanium compound and the polyvalent carboxylic acid and / or anhydride thereof is preferably in the range of 2/1 to 0.4 / 1. A particularly preferable range is 1/1 to 0.5 / 1.

［上記式中、ｎは２〜４の整数を表わす。］

[In the above formula, n represents an integer of 2 to 4. ]

  After the above two types of catalyst systems are produced by the above-described method, they can be used as a polyester polycondensation catalyst by the same operation using the same amount as that of other commonly used polyester catalysts.

EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention does not receive any limitation by this. In addition, each value in an Example was calculated | required with the following method.
1) Intrinsic viscosity (IV)
After 0.6 g of polyethylene terephthalate was dissolved by heating in 50 cc of o-chlorophenol, it was once cooled and calculated from the solution viscosity of the solution measured at 35 ° C. using an Ubbelohde viscometer.
2) Hue (Col)
Polyethylene terephthalate is sampled from the reactor in a molten state, sandwiched between metal plates, and cooled with water to obtain a disk-shaped polymer sample. This was heat-treated in a dryer at 140 ° C. for 60 minutes for crystallization, and then measured with a CM-7500 type color machine manufactured by Color Machine Co., Ltd. The sample after the solid phase was measured in the same manner without the heat treatment step. Yellowness was evaluated by the Col-b value.
3) Diethylene glycol (DEG) content The sample was decomposed with hydrazine hydrate and measured by gas chromatography (GC).

[Reference Example 1]
In a reactor equipped with a stirrer, 38000 parts by mass of ethylene glycol and 46 parts by mass of acetic acid were placed in a nitrogen atmosphere, and 325 parts by mass of tetra-n-butoxytitanium was slowly added gradually and maintained at 50 ° C. for 1 hour. Thus, an ethylene glycol solution of a titanium compound was obtained (hereinafter, this solution is referred to as “TBT / EG solution”). A solution obtained by dissolving 294 parts by mass of monobutyl phosphate in 1700 parts by mass of ethylene glycol was gradually added thereto, and after addition of the whole amount, the reaction was carried out at a temperature of 100 ° C. for 1 hour to produce a tetra-n-butoxytitanium / monobutyl phosphate reaction. A product suspension was obtained (hereinafter referred to as TBT-MBP solution). When heated at 100 ° C. in this ethylene glycol, the gram equivalent ratio of phosphorus atoms to titanium atoms (P / Ti) was 2.0.

[Reference Example 2]
In a reactor equipped with a stirrer, 919 parts by mass of ethylene glycol and 80 parts by mass of trimellitic anhydride were placed in a nitrogen atmosphere and mixed and stirred. Then, 71 parts by mass of tetra-n-butoxytitanium was slowly added gradually to obtain a transparent solution. An ethylene glycol solution of titanium compound (hereinafter referred to as TMT solution) was obtained. The reaction molar ratio of tetra-n-butoxytitanium and trimellitic anhydride was ½.

[Example 1]
254 parts by mass of bis- (2-hydroxyethyl) terephthalate (BHET) manufactured by Tokyo Chemical Industry Co., Ltd., and a titanium compound suspension of a reference example as a polymerization catalyst were charged in a reactor under a nitrogen atmosphere and normal pressure. The molar ratio of the titanium element to 4 × 10 ⁻⁵ was added.
Next, the temperature is set to 285 ° C., 10 minutes at normal pressure, 10 minutes at 4 kPa, and 40 minutes at 0.4 kPa for 40 minutes, respectively. A condensation reaction was performed. No oligomer blockage or the like in the distilling portion occurred. Table 1 shows the quality of the produced polyethylene terephthalate.

[ Reference Example 12 ]
In Example 1, instead of the TBT-MBP solution, a TMT solution was used as a polymerization catalyst, and trimethyl phosphate was added so that the phosphorus element with respect to the charged moles of BHET was also in a molar ratio of 8 × 10 ^−5. The same operation was performed. No oligomer blockage or the like in the distilling part occurred during the polymerization reaction. Table 1 shows the quality of the produced polyethylene terephthalate.

[ Reference Example 13 ]
In Example 1, instead of the TBT-MBP solution, the TBT / EG solution described in Reference Example 1 was used as a polymerization catalyst, and trimethyl phosphate had a molar ratio of 8 × 10 ^{−5 with} respect to the number of moles of BHET charged with phosphorus. The same operation was performed except that it was added so that No oligomer blockage or the like in the distilling part occurred during the polymerization reaction. Table 1 shows the quality of the produced polyethylene terephthalate.

[Comparative Example 1]
In Example 1, instead of the TBT-MBP solution, germanium dioxide has a molar ratio of germanium element to the charged mole of BHET of 20 × 10 ⁻⁵ , and trimethyl phosphate has a molar ratio of phosphorus element to the charged mole of BHET of 20 The same operation was carried out except that it was used so as to be × 10 ^−5, and when the polymerization reaction stage was started at 0.4 kPa, the reaction was stopped because oligomer blockage in the distilling portion occurred. The reaction was repeated under normal pressure for 20 minutes, 4 kPa for 20 minutes, and 0.4 kPa for 80 minutes to obtain polyethylene terephthalate. The quality is shown in Table 1.

[Comparative Example 2]
In Example 1, instead of the TBT-MBP solution, the antimony trioxide has a molar ratio of antimony element to the mole number of BHET of 27 × 10 ⁻⁵ , and trimethyl phosphate has a molar ratio of phosphorus element to the mole number of BHET of When the same operation was performed except that it was used so as to be 34 × 10 ⁻⁵ , when the polymerization reaction stage under 0.4 kPa was entered, the oligomer was blocked in the distilling portion, and thus the reaction was stopped. The reaction was repeated under normal pressure for 20 minutes, 4 kPa for 20 minutes, and 0.4 kPa for 50 minutes to obtain polyethylene terephthalate. The quality is shown in Table 1.

[Comparative Example 3]
In Example 1, instead of the TBT-MBP solution, the same operation was performed except that trisacetylacetonato aluminum was used so that the molar ratio of aluminum element to the charged mole number of BHET was 30 × 10 ⁻⁵ . However, when the polymerization reaction stage was started at 0.4 kPa, the reaction was stopped because oligomer blockage in the distilling portion occurred. The reaction was repeated under normal pressure for 20 minutes, 4 kPa for 20 minutes, and 0.4 kPa for 82 minutes to obtain polyethylene terephthalate, but the viscosity was very low and the reactivity was insufficient. The quality is shown in Table 1.

  According to the method of the present invention, polyethylene terephthalate can be obtained at a good polymerization rate using only polyethylene terephthalate made from bis- (2-hydroxyethyl) terephthalate as a raw material and without adding other polyester monomers such as terephthalic acid. . In addition, since the polymerization reaction can proceed smoothly without causing blockage by scattered oligomers, its industrial significance is great.

Claims (2)

A method for producing polyethylene terephthalate in which only bis- (2-hydroxyethyl) terephthalate is polymerized using a titanium compound as a catalyst , wherein the titanium compound is represented by the following general formula (I) and the following general formula (IV): Production of polyethylene terephthalate using a precipitate obtained by heating a phosphorus compound represented by) in glycol in a range where the gram equivalent ratio of phosphorus atom to titanium atom (P / Ti) is 1 to 4. Way .

[In the above formula, R ¹ , R ² , R ³ and R ⁴ are the same or different and each represents an alkyl group having 1 to 10 carbon atoms or a phenyl group; In the case of 2, 3 or 4, 2, 3 or 4 R ² and R ³ may be the same or different from each other. ]

[In the above formula, R ⁸ is an alkyl group having 2 to 18 carbon atoms or an aryl group having 6 to 20 carbon atoms, p is 1 or 2, and when p is 1, q is 0 or 1, and p is When 2, q is 0. ] As a titanium compound, a titanium compound represented by the following general formula (I), or a titanium compound represented by the following general formula (I) and an aromatic polyvalent carboxylic acid represented by the following general formula (II) or its anhydride The method for producing polyethylene terephthalate according to claim 1, wherein a polymerization catalyst system comprising a titanium compound component containing at least one selected from the group consisting of products obtained by reacting a product is used.

[Wherein R ¹ , R ² , R ³ and R ⁴ are the same or different and each represents an alkyl group having 1 to 10 carbon atoms or a phenyl group, m represents an integer of 1 to 4, and m represents In the case of 2, 3 or 4, 2, 3 or 4 R ² and R ³ may be the same or different from each other. ]

[In the above formula, n represents an integer of 2 to 4. ]